Method and apparatus to inspect hoisting ropes

ABSTRACT

A hoisting rope for an elevator includes a plurality of longitudinally spaced, discrete targets retained within the rope. The targets have a characteristic that may be monitored by a device that is responsive to that characteristic. In a particular embodiment, the targets are formed from a magnetically permeable material and the monitoring device responds to changes in the magnetic field as the target passes the monitoring device. In another embodiment, the targets are formed from material that reflects electromagnetic energy. In this embodiment, the monitoring device emits electromagnetic energy and is sensitive to the energy that is reflected back from the target. A method to inspect the hoisting ropes includes the steps of positioning the monitoring device proximate to the hoisting rope, moving the hoisting rope relative to the device, and monitoring the targets to determine the spacing between targets. Changes in spacing are indicative of stretching of the rope, and thereby degradation of the rope.

This is a division of copending application Ser. No. 08/781,944 filedDec. 20, 1996, the contents of which is incorporated herein byreference.

TECHNICAL FIELD

The present invention relates to roped elevator systems, and moreparticularly to a method and apparatus to inspect the hoisting ropes ofsuch systems.

BACKGROUND OF THE INVENTION

Hoisting ropes for elevators are used to provide the necessary liftingforces and traction forces for moving the elevator car. Hoisting ropesare typically formed from steel wire strands woven together to form therope. Such hoisting ropes have proven to be very durable and dependable.A drawback to the use of steel wire ropes is their weight. As the riseof the elevator increases, the portion of the load resulting from therope weight increases. This produces a limitation on the rise of theelevator and the size of the lifting equipment.

Other high strength materials have been suggested to replace the steelwire ropes. High strength, polyaramid materials, such as KEVLAR, arebeing investigated for use in elevator applications. These ropes wouldbe formed from polyaramid fibers woven to form strands, which are thenwoven together to form the rope. An outer jacket may then be used toprotect the woven fibers from damage and wear, and to provide thenecessary traction to move the elevator car.

An area of concern is how to inspect such synthetic ropes to determineif the rope should be discarded and replaced with a new rope. Thecurrent inspection methods for steel wire rope includes visuallyinspecting the rope to determine the number of broken steel fibers in agiven length of steel rope. If a predetermined maximum number of brokenfibers is detected, the steel rope is discarded. This method is notapplicable to synthetic fiber ropes having an outer jacket.

One previously known method is to place an electrically conductivemember within the rope. The status of the conductive member may betested by applying an electrical current to the member. If damage occursto an extent great enough to break the conductive member, the electricalcircuit is broken. There are several drawbacks to this method. First,there is no assurance that the loss of electrical continuity is theresult of damage to the rope. Second, there is no qualitativeinformation to indicate if the rope is degrading during use. The firstindication is provided by the broken conductive member. Further, thismethod provides no information on the location of the damage along thelength of the rope.

The above art notwithstanding, scientists and engineers under thedirection of Applicants' Assignee are working to develop methods andapparatus to inspect hoisting ropes.

DISCLOSURE OF THE INVENTION

The present invention is predicated in part upon the recognition that asa hoisting rope degrades, the fibers and strands begin to fail. Thiswill cause the remaining fibers and strands to carry less loads, whichwill lead to elongation of those fibers and strands. Monitoring theelongation of the rope provides an indication of the level ofdegradation of the rope.

According to the present invention, a hoisting rope includes a pluralityof longitudinally spaced, discrete targets retained within the rope. Thetargets have a characteristic that may be monitored by a deviceresponsive to that characteristic.

According to another aspect of the invention, a method to inspecthoisting ropes includes the steps of positioning the device proximate tothe hoisting rope, moving the hoisting rope relative to the device, andmonitoring the targets to determine the spacing between targets.

The feature of targets disposed within the rope provides the advantageof being able to monitor the rope without requiring visual inspection ordestructive evaluation. The monitoring device senses each target whenthe target is proximate to the device. The spacing between targets isthen monitored for changes. For example, if a particular section of ropebegins to degrade, that section may begin to stretch as fewer strandsand fibers begin to carry the load. Stretching of this section of therope will cause the targets in that section to move further apart. Whenthis section of the rope is monitored by the device, the increase inseparation between targets will be recognized.

Further advantages of the invention include that the device may be usedto periodically inspect the ropes, or the device may be placed in afixed position near the ropes and used to continually monitor the ropes.The latter embodiment is particularly advantageous for elevatorapplications, since the monitoring information may be communicated withthe controller of the elevator. If significant degradation of the ropeis sensed, the operation of the elevator may be stopped. In addition,the output of the monitoring device may be communicated to a remotemonitoring system such that maintenance or replacement of the ropes maybe conducted prior to significant degradation of the ropes.

In a particular embodiment, the plurality of targets are disposed withinan elastic tube, with the targets being spaced apart by spacers disposedbetween adjacent targets. The elastic tube is not a load-carrying memberof the rope and has a modulus of elasticity less than the load-carryingstrands of the rope. This permits the tube to stretch in accordance withthe amount the rope elongates. The spacers do not have the particularcharacteristic that is being monitored by the monitoring device and areused to provide a predetermined spacing between adjacent targets.

In one particular configuration, the targets are formed from materialhaving a magnetic permeability. In this configuration, the monitoringdevice is sensitive to changes in magnetic fields such that it respondsto the targets. In another particular configuration, the targets areformed from material that reflects electromagnetic waves. In thisconfiguration, the monitoring device emits electromagnetic energy and issensitive to the energy that is reflected back to the monitoring device.According further to this configuration, the targets may be shaped toprovide reflected energy of a particular frequency in a preselecteddirection, such as lateral to the longitudinal direction of the rope.This latter embodiment provides means to filter out unwanted noise thatmay interfere with the operation of the monitoring device and reducesradiated power needed to detect the target.

The foregoing and other objects, features and advantages of the presentinvention become more apparent in light of the following detaileddescription of the exemplary embodiments thereof, as illustrated in theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of an elevator system.

FIG. 2 is a sectional side view of a length of a single rope having aplurality of targets embedded therein.

FIG. 3 is a sectional view taken along line 3--3 of FIG. 2.

FIG. 4 is a side view of a flexible tube having the targets and spacers.

FIGS. 5-7 are views of different shaped targets. FIG. 5 shows acylindrical shaped target; FIG. 6 shows targets having a hyperbolicconical shape; and FIG. 7 shows targets having an oblate spheroid shape.

FIG. 8 is an illustration of an alternate embodiment having a singlemonitoring device to monitor a plurality of ropes.

BEST MODE FOR CARRYING OUT THE INVENTION

Illustrated in FIG. 1 is an elevator system 12 having a car 14 connectedto a counterweight 16 by a plurality of ropes 18. The ropes 18 extendover a traction sheave 22 that is driven by a machine 24. Tractionbetween the sheave 22 and the ropes 18 drives the car 14 andcounterweight 16 through the hoistway. Operation of the machine 24 iscontrolled by a controller 26. The controller 26 receives inputs from aposition sensing device 28 to determine the speed and position of thecar 14.

Also illustrated in FIG. 1 is a rope monitoring system 32. The ropemonitoring system 32 includes a monitoring device 34 disposed in alocation proximate to the ropes 18. The monitoring device 34 senses thepresence of targets 36 (see FIG. 2-4) disposed within the ropes 18. Inthe embodiment shown, the monitoring device 34 is an inductive sensorthat responds to changes in the magnetic field within the field ofresponse of the device 34. As shown in FIG. 1, the monitoring device 34produces an output that is communicated to the controller 26.

Referring now to FIGS. 2 and 3, each rope 18 is formed from a pluralityof load-carrying strands 38 of a synthetic fiber, such as KEVLAR.Captured within the strands 38 of the rope 18 is a plurality of thetargets 36. The targets 36 are spaced longitudinally throughout the rope18 at a predetermined distance apart. The targets 36 are centrallylocated within the rope 18 and are retained within a flexible tube 40,as shown in FIG. 4. The tube 40 is not a load-carrying member of therope 18. A plurality of flexible spacers 42 are placed between adjacenttargets 36 to maintain the proper spacing between targets 36 at the timeof installation. The necessary spacing between adjacent targets 36 isdependent upon the discrimination of the monitoring device 34 to thetargets 36. Once installed, shear forces from the surrounding strands ofthe ropes 18 will provide further retention of the targets 36.

The targets 36 are formed from a ferrous material such that each target36 affect the magnetic flux that is generated and detectable by themonitoring device 34. A suggested material for the targets 36 is steel,although other ferrous materials may be equally applicable. Each target36 is spherically shaped to avoid damage to the surrounding fibers ofthe strands 38. The tube 40 and the spacers 42 are formed from materialsthat do not emit magnetic flux and that have a modulus of elasticityless than the strand 38 material and strain-to-failure propertiesgreater than the strand material. In this way, the tube 40 will stretchin accordance with the strands 38 during operation of the elevatorsystem 12 and over the life of the rope 18. The tube 40 and spacers 42are one example of a means to locate the targets 36 within the rope 18.Other possible means of locating the targets include weaving the targetsinto the rope during the fabrication of the rope, or weaving a strandformed from alternating ferrous and non-ferrous materials into thestrands. In addition, the tube is shown in FIGS. 2 and 3 as beinglocated in the center of the rope. The tube may also be integrated intothe rope such that it follows the helix or twist of the stranded rope.

During operation, the controller 26 communicates with the machine 24 torotate the traction sheave 22 in the desired direction. Traction forcesbetween the sheave and the ropes 18 move the car 14 and counterweight 16in opposite directions. As the ropes 18 are driven, the plurality oftargets 36 move past the monitoring device 34. Each target 36 triggers achange in the magnetic field that is sensed by the monitoring device 34.The monitoring device 34 senses the amount of time between adjacenttargets 36. The time between targets 36 is correlated with the speed ofthe car 12, as determined by the position sensing device 28, todetermine the distance between adjacent targets 36. The determineddistance between targets 36 is then compared to the known distancebetween targets 36 at the time of installation. If the rope 18 haselongated in a particular section of the rope 18, which is indicative ofdegradation of the rope 18, the targets 36 in that section will alsohave moved further apart. Therefore, the increased distance betweentargets 36, as compared to the known, installed distance between targets36, is indicative of degradation of the rope 18. In addition,correlation of the monitoring device 34 output and the output from theposition sensing device 28 provides a determination of the location ofthe damaged section of the rope 18.

The output of the monitoring device 34 is communicated to the controller26. The controller 26 compares the determined distance between adjacenttargets 36 with a predetermined threshold to determine if thedegradation of the rope 18 is sufficient such that the elevator system12 should be shut down. If not sufficient to warrant shutting down theelevator system 12, the controller 26 compares the elongation to anotherthreshold to determine if it is sufficient to warrant an inspection ofthat particular section of rope 18. In addition, the data generated bythe monitoring device 34 may also be communicated out to a remotemonitoring system 44 for further analysis and/or to provide theinformation to a mechanic to use during a maintenance visit to theelevator system 12. During a maintenance visit, the mechanic can use theinformation to conduct a visual inspection of the degraded portion ofthe rope 18, such as measuring the diameter of the rope 18 or lookingfor visual signs of damage.

Although shown and described as a monitoring system for continuouslymonitoring the health of the ropes, the invention is equally applicableas a method to periodically inspect the health of the ropes. In thisconfiguration, a mechanic would install a monitoring device during aroutine maintenance visit. As the elevator system is cycled through thehoistway, the distance between adjacent targets is determined. Theinformation on elongation is then compared to the predetermined baselinedistance between targets, and to previous information generated duringprevious maintenance visits, to determine if any significant degradationhas occurred.

The monitoring system 32 described above, which uses changing magneticfields to determine position of the targets 36, is one embodiment of theinvention. Another embodiment is illustrated in FIG. 8. In thisembodiment, the monitoring system 50 includes targets 52 formed fromdiscrete conductive members spaced longitudinally throughout the ropes54 and a monitoring device 56 that generates high frequency (2 gHz to 40gHz) radar directed at the plurality of ropes 54. The targets 52, asthey pass the monitoring device 56, reflect the electromagnetic waves ina narrow beam that extends laterally from the rope 54 and is received bythe monitoring device 56. The targets 52 may be relatively long (5-200cm) and thin (0.05-1 mm) and shaped in a cylindrical manner 52a as shownin FIG. 5. As an alternative, the targets 52 may have various othershapes, such as a hyperbolic conical shape 52b (see FIG. 6) or a oblatespheroid shape 52c (see FIG. 7). Targets of various shapes will providedifferent response patterns that may be more advantageous depending onthe operating conditions and the sensitivity of the monitoring device56.

The targets 52 are retained within a thin wall elastic tube 58 formedfrom a non-reflecting material at the frequencies being generated by themonitoring device 56. As with the embodiment of FIGS. 1-4, the tube 58has a modulus of elasticity less than the strands of the rope 54 suchthat it freely stretches as the strands elongate.

The monitoring device 56 is a multiple impulse radar that is positionedproximate to the plurality of ropes 54. The pulse repetition frequencyis high (approximately 2 mHz) such that the targets 52 may bedistinguished from the rope 54 and any irregularities in the spacingbetween targets 52 may be determined. In addition, the pulsed radaremitted by the monitoring device 56 may be focused at a variouspredetermined distances. As a result, a plurality of ropes 54 may bemonitored simultaneously using a single monitoring device 56.

Although the invention has been shown and described with respect toexemplary embodiments thereof, it should be understood by those skilledin the art that various changes, omissions, and additions may be madethereto, without departing from the spirit and scope of the invention.

What is claimed is:
 1. An elevator system including a remote elevatormonitoring system and a rope monitoring device, the rope monitoringdevice providing an output signal indicative of the level of degradationof the rope, wherein the output signal is transmitted to the remoteelevator monitoring system for a determination of the need formaintenance or replacement of the rope.
 2. The elevator system accordingto claim 1, wherein the elevator monitoring system produces a servicealert if the level of degradation of the rope exceeds a predeterminedthreshold.
 3. The elevator system according to claim 1, furtherincluding a controller, wherein the output signal is transmitted to thecontroller, and wherein the controller shuts down the elevator system ifthe level of degradation of the rope exceeds a predetermined threshold.4. A method to monitor rope degradation of an elevator system, theelevator system including a rope monitoring device and a remote elevatormonitoring system, the method including the steps of:monitoring the ropeto determine the level of degradation of the rope; outputting a signalcorresponding to the level of degradation of the rope; and transmittingthe output signal to the remote elevator monitoring system.
 5. Themethod according to claim 4, further including the step of producing aservice alert if the rope monitoring device determines that the level ofdegradation of the rope exceeds a predetermined threshold.
 6. The methodaccording to claim 5, further including the step of dispatching amechanic to the site of the elevator system.
 7. The method according toclaim 4, further including the step of dispatching a mechanic to thesite of the elevator system.
 8. The method according to claim 4, whereinthe elevator system further includes a controller, the method furtherincluding the steps of:transmitting the output signal to the controller;and shutting down the elevator system if the level of degradation of therope exceeds a predetermined threshold.